Mismatches in nutrient composition (e.g., protein, carbohydrates, lipids, etc.) between consumers and the resources they depend on can have ecological consequences, affecting traits from individual behavior to community structure. In many terrestrial ecosystems, ants depend on plant and insect mutualist partners for carbohydrate-rich rewards that are nutritionally unbalanced (especially in protein) relative to colony needs. Despite imbalances, many carbohydrate-feeding ant mutualists dominate communities—both competitively and numerically—raising the question of whether excess carbohydrates ‘fuel’ colony acquisition of limiting resources and growth. In a 10-month field study, we manipulated carbohydrate access for the obligate plant-ant Crematogaster nigriceps to test whether carbohydrate availability could be mechanistically linked to ecological dominance via heightened territory defense, increased protein foraging, and colony growth. Supplementation increased aggressive defense of hosts after only two weeks, but was also strongly linked to variation in rainfall. Contrary to predictions, we did not find that supplemented colonies increased protein foraging. Instead, colonies with reduced carbohydrate access discovered a greater proportion of protein baits, suggesting that carbohydrate deprivation increases foraging intensity. We found no significant effect of carbohydrate manipulation on brood or alate production. These results contrast with findings from several recent short-term and lab-based nutrient supplementation studies and highlight the role of seasonality and biotic context in colony-foraging and reproductive decisions. These factors may be essential to understanding the consequences of carbohydrate access in natural plant-ant systems.